Various new light-emitting device technologies have started emerging. For example, U.S. patent publication 2012/0112165 proposes a quantum well LED which uses nonradiative energy transfer (NRET) to improve device efficiency. However, commercially this kind of NRET based quantum well LED has been largely unsuccessful to date. This may be because of the difficulty to integrate the NRET structures within the quantum well LEDs using current process technology, and the resulting NRET efficiency is poor due to geometrical reasons.1 2,3 
Nanocrystal quantum dots (NQDs), are a more promising class of disordered semiconductor colloidal materials4,5, as they may offer size tunable emission spectra, high photoluminescence (PL) quantum yields, narrow emission full-widths-at-half-maxima (FWHMs) and increased environmental stabilities at reduced costs. Prior art NQD-based electroluminescent devices6,7,8, commonly rely charge injection pumping of the NQDs. However, charge injection and transport across the NQD thin films are weak, due to passivating and stabilizing organic ligands9,10,11, and unbalanced, due to different potential barriers for electrons and holes leading to Auger recombination.
As an alternative, organic LEDs (OLEDs) can in principle reach large peak external quantum efficiencies (reported up to 6.3%12 for fluorescence based OLEDs and 18%13 for phosphorescence based OLEDs) with proper charge injection and blocking layers. However, polymer based OLEDs may suffer from forbidden emission from the triplet state excitons.
Phosphorescent LEDs are another alternative capable of harvesting triplet excitons, but they may be expensive due to the heavy metal ions used for phosphorescence.